Means for preventing or inhibiting galloping vibrations in overhead transmission lines

ABSTRACT

In combination with a transmission line conductor suspended from a stationary support structure to which it is connected at a plurality of longitudinally spaced points, the suspended conductor defining a torsionally oscillating system, torsional restraint means connected to or incorporated in the conductor at each span intermediate said spaced points for limiting torsional movements whereby to prevent build up of galloping vibrations.

[ Dec. 11, 1973 Great Britain..1................1.... 174/42 OTHERPUBLICATIONS Burgess et al., AIEE Technical Paper 51-205, The

Torsional Damper for Conductors-Service Experience and FurtherExperimental Work, published May 1951, 8 pages.

834,931 2/1970 Canada................................. 616,802 11/1926France.................... 708,630 5/1931 France......... 398,516 7/1924Germany 805,872 12/1958 Primary Examiner-Laramie E. Askin Attorney-J. A.Legris et a1.

[57] ABSTRACT In combination with a transmission line conductorsuspended from a stationary support structure to which it is connectedat a plurality of longitudinally spaced points, the suspended conductordefining a torsionally GALLOPING VIBRATIONS IN OVERHEAD TRANSMISSIONLINES Olaf Nigol, 272 Markland Dr., Etobicoke, Ontario, Canada Mar. 23,1972 Appl. No.: 237,380

174/42, 174/130 Int. H02g 7/14, I-IOIb 5/08 [58] Field ofSearch....................i. 174/42, 108, 127, 174/128, 129 R, 130, 131R, 131 A, 131 B; 188/1 B, 266, 268

References Cited UNITED STATES PATENTS 174,42 oscillating system,torslonal restraint means connected 174,42 to or incorporated in theconductor at each span inter- 7 42 mediate said spaced points forlimiting torsional movements whereby to prevent build up of gallopingvibratlons.

n u u n n 1 Ridgers et FOREIGN PATENTS OR APPLICATIONS WLL aa tt mmmnnuuumm m m othh cc .lr UU BCABB 4 83028 5623445 9999999 1111111 973929 1460157 0906437 496 5 9 9970174 6 6 2 8 221 222 6 B0 7 VL @0555/2 2 FOAMN m r w H W 0 L M4 TEE/AL 12 Claims, 9 Drawing FiguresCanada................................. 174/42 ALUM/N/UM 52 55 V5 7// L0W FAB/6 770/1/ A T542 ML LOW Fle/tr/o/v MA 75/2/44 PATENTEHUEC 1 1 msSHEET 10F 2 LOW FE/CT/O/V MATE/Z/AL w W L A SLEEVE BUTYL EUEBE/Z FOAMMEANS FOR PREVENTING R INIIIBITING GALLOPING VIBRATIONS IN OVERHEADTRANSMISSION LINES This invention relates to a system for preventing orinhibiting the build up of galloping vibration in overhead transmissionlines.

The seriousness of conductor vibration in overhead transmission lineshas been recognized for many years, and many attempts have been made tocontrol it. Evidence has shown that when conductor vibration is leftuncontrolled it will result in fatigue failure of conductors; largeamplitude vibrations may also lead to structural damage in line supportsand the like. Furthermore, the occurrence of large amplitude vibrationsmakes it necessary to provide adequate clearance between the phaseconductors of a transmission line to prevent flash-over, a measure whichinvolves considerable cost.

Conductor vibration in overhead transmission lines is dividedarbitrarily into two categories: galloping and aeolian vibration. Theterm galloping is applied to large amplitude, low frequency vibrations,induced in most cases by wind action on aerofoils. The term aeolian isapplied to relatively small amplitude, high frequency, vibrations alsoinduced by wind action but in a different manner. The present inventionis concerned primarily with vibrations of the former type.

Investigations made by the inventor into the nature of gallopingvibrations have shown that such vibrations in iced conductors areinitiated and maintained bytorsiona] instability and oscillation of theconductors. Briefly, the excitation mechanism may be described in thefollowing way. As ice deposits on the windward side of a conductor itproduces a torsional load which causes the conductor to rotate. Theangle of rotation or twist depends upon the amount of ice deposited, theshape of the deposit, and the natural torsional stiffness of theconductor. Since the torsional stiffness of the conductor variesinversely with the distance from the torsionally rigid suspensionpoints, the angle of rotation will be greatest for the centre portion ofthe span. Now the eccentric ice load deposited on the conductor acts asan aerofoil which, when acted upon by the wind, exhibits definiteaerodynamic moment, drag and lift characteristics. The moment and liftforces are the most significant in relation to galloping. The magnitudesof these aerodynamic forces are directly proportional to the squareofthe wind speed, and are largely dependent upon the orientation of theice-formed aerofoil.

In considering the natural torsional stiffness of the conductor, themoment due to the eccentric ice load, and the aerodynamic moment of theiced conductor, one finds that the effective torsional stiffness of theconductor span becomes very low for a range of wind speeds and amountsof ice deposited. A low effective torsional stiffness results in lowfrequency torsional oscillations with several aerofoil orientations.When the torsional frequency coincides with, or is an odd multiple of,one of the resonant translational frequencies, the two modes ofvibration will become strongly coupled and galloping will occur.

Now the amount of ice required to rotate the conductor to a criticalorientation in the centre of the span is directly proportional to thenatural torsional stiffness of the conductor span and hence inverselyproportional to the span length. Consequently, a short span will supporta heavier ice load than will a long span before a critical orientationis reached. A short span will also require a higher aerodynamic momentand hence a higher wind velocity before it becomes torsionally unstable.Therefore, one solution to the problem of galloping would be to shortenthe conductor spans.

It is an object of the present invention to provide an alternativesolution to the problem, based on the above considerations, which iscompatible with present design practice wherein the conductor spans maybe of considerable length.

Basically, the present invention provides in combination with atransmission line conductor suspended from a stationary supportstructure to which it is connected at a plurality of longitudinallyspaced points, the suspended conductor defining a torsionallyoscillating system, torsional restraint means connected to the conductorat each span intermediate said spaced points, or incorporated in theconductor, for limiting torsional movements whereby to prevent build upof galloping vibrations. The torsional restraint means may be adapted todissipate vibrational energy frictionally between relatively slidablesurfaces, or in a body of damping material such as butyl rubber foam, ormay be arranged so as to alter the characteristics of the torsionallyoscillating system so as to prevent coupling between the torsional andtranslational modes of oscillation.

In order that the invention may be readily understood, severalembodiments thereof will now be described by way of example withreference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic side view showing one span length of aconductor in an overhead transmission line;

FIG. 2 is a longitudinal sectional view of a torsional restraint meansaccording to one embodiment of the invention;

FIG. 3 is a cross sectional view of the torsional restraint means ofFIG. 2;

FIG. 4 is a longitudinal sectional view of a torsional restraint meansaccording to a second embodiment of the invention;

FIG. 5 shows in side elevation a torsional restraint means according toa third embodiment of the invention;

FIG. 6 shows an end elevation of the torsional restraint means shown inFIG. 5; and

FIGS. 7, 8 and 9 are cross sectional views of three different strandedconductor configurations embodying the invention.

Referring to FIG. 1, which may be read in conjunction with each of theembodiments described below, an overhead transmission line comprises aconductor 10 suspended from a stationary support structure 11, whichwould typically comprise masts or towers. The conductor is connected tothe support structure at longitudinally spaced points, defining the spanlengths, by support insulators 12; these insulators are conventionallysuspended from transverse arms on the masts or towers. In general such atransmission line would comprise a number of such conductors, spacedfrom one another, but for ease of illustration only one conductor isshown in the drawings. Torsional restraint means are connected to theconductor at each span intermediate the support insulators. Devices ofthe type shown in FIGS. 2 and 3, FIG. 4, or FIGS. 5 and 6 may beconnected to the conductor at the position A midway between the ends ofthe span, or alternatively in the case of long spans at the positions Bwhich are respectively one third, and two thirds of the distance alongeach span. Instead of restraining the conductor at discrete points,however, torsional restraint means may be distributed along the lengthof the conductor, such means being illustrated in FIGS. 7, 8 and 9.

Referring now to FIGS. 2 and 3, the torsional restraint deviceillustrated comprises a first body 13 in the form of an aluminum splittubular sleeve, the two halves of the sleeve being clamped together bybolts 14 so as to engage the conductor securely. The outer cylindricalsurface of the sleeve 13 is coated or clad with a layer of low frictionmaterial 15, that is to say, a material having a very low coefficient offriction, such as polytetrafluoroethylene, which provides a firstfriction surface. Connected to the sleeve 13 is asecond body 16 in theform of an aluminum split clamp; this clamp comprises a pair of clampmembers connected together by a hinge 17, and secured by means of aspring-loaded adjustable bolt 18 whereby the clamping pressure on thesleeve can be adjusted. The clamp 16 provides an inner surface which iscoated with a layer of low friction material 19, this layer providing asecond friction surface disposed in sliding engagement with the firstfriction surface of the layer 15. Torsional movements of the clamp 16are restrained by means of a cast iron weight 20, suspended from theclamp 16. It is found in practice that the centre of gravity of theweight 20 should be as close as possible to the axis of the conductor10, and usually not more than about six inches therefrom. The weight maybe up to 60 pounds, but may be varied over a range according toconductor diameter; typically, for a single weight per span the weightmay be five pounds for a half inch diameter conductor and about 50pounds for a two and a half inch diameter conductor.

In a variant of the embodiment described above the first and secondbodies are replaced by a stack of coaxial aluminum discs, the discsbeing secured alternatively to the conductor and to the weight, and thecooperating faces of the discs being coated with low friction materialand providing the relatively slidable surfaces. In this variant thediscs are clamped together under axial pressure.

In the embodiment of the invention described above, and in its variant,torsional movement of the conductor 10 results in relative slidingmovement of the surfaces of the layers l5, 19, the kinetic energy ofsuch movement being dissipated frictionally.

Referring now to FIG. 4, the torsional restraining means of the secondembodiment comprises a cylindrical body 21 of resiliently deformablematerial having a high coefficient of internal damping butyl rubber foamis most suitable for this purpose firmly clamped onto the conductor 10by a clamp 16. The clamp 16 is of the same construction as the clampshown in FIGS. 2 and 3, and is restrained against torsional movements bya weight 20 suspended from the clamp.

In this embodiment, the kinetic energy of torsional movement of theconductor 10, instead of being dissipated frictionally betweenrelatively slidable surfaces, is absorbed within the body 21 by elastichysteresis.

In the embodiment shown in FIGS. 5 and 6, a split aluminum clamp 22 isclamped securely onto the conductor 10, the clamp 22 providing a clamphinge 23 and clamping bolts 24. The clamp is restrained against rotationby a weight 20 suspended from the clamp. In this case the weighted clampprovides a high inertial restraint at the point of the conductor towhich it is secured, thus in effect altering the characteristics of thetorsionally oscillating system. In this way the torsional andtranslational modes of vibration are decoupled.

In the embodiments illustrated by FIGS. 7, 8 and 9 torsional restraintmeans are distributed along the length of the conductors. The conductorshown in FIG. 7 comprises an inner layer of conductor strands 25 whichare loosely filled within a flexible tubular sleeve 26, and an outerlayer of conductor strands 27 extending along the length of the outersurface of the sleeve in engagement with it. The strands are coated withlow friction material, such as the material known by the trade markTeflon, and the sleeve is of the same material. In this case kineticenergy resulting from torsional movements is dissipated frictionallybetween the relatively slidable surfaces of the coated conductorstrands. I

In the embodiment of FIG. 8, the conductor strands 28 are coated withthe low friction material and are loosely fitted within a tubularplastic or metal sleeve 29.

In the embodiment of FIG. 9 the conductor comprises an inner layer ofconductor strands 30 and an outer layer of conductor strands 31, on asleeve 32 of high damping material such as butyl rubber foam separatingthe layers and being firmly engaged thereby so that relative torsionalmovements between the layers subject the sleeve to torsional shear. Inthis way the kinetic energy of such movements is absorbed in the body ofthe sleeve.

Although the invention has been particularly described with reference tosingle conductors, it is equally applicable to bundle conductorarrangements. In such an application the individual conductors of abundle may be held in a fixed spatial relationship at each of saidspaced points by means of a rigid spacer, each conductor being securedto the spacer by means for damping torsional movement of the conductorrelative to the spacer. The damping means may provide a pair ofrelatively slidable friction surfaces, as described with reference toFIGS. 2 and 3, or alternatively a deformable body of butyl rubber foamas described with reference to FIG. 4.

What I claim as my invention is:

1. In combination with a transmission line conductor suspended from astationary support structure to which it is connected at a plurality oflongitudinally spaced points, the suspended conductor defining atorsionally oscillating system, torsional damping means connected to theconductor at each span intermediate said spaced points at a distance notless than one third of the length of the span from the nearer of saidpoints, each said damping means comprising a first body rigidlyconnected to the conductor, the first body providing a first frictionalsurface arranged coaxially with the conductor, a second body connectedto the first body, the second body providing a second frictional surfacedis-' posed first body comprises a tubular metallic sleeve secured tothe conductor, the sleeve having a coating of low friction materialdefining said first surface, and the second body comprises a clamp whichis clamped onto the sleeve, the clamp providing a sleeve-engaging suracewhich is coated with said low frictional material. in sliding contactwith the first frictional surface, said first and second frictionalsurfaces being defined by coatings of low friction material on saidfirst and second bodies, and means attached to said second body forrestraining torsional movement of the second body so as to permitrelative sliding movements between said surfaces.

2. The combination claimed in claim 1, wherein the 3. The combinationclaimed in claim 2, wherein the clamp comprises a pair of hingedlyconnected clamping members secured by a spring-loaded adjustable boltfor adjustment of the clamping pressure.

4. The combination claimed in claim 1, there being one said dampingmeans to each span of the transmission line conductor positioned midwaybetween a respective pair of said longitudinally spaced points.

5. The combination claimed in claim 1, there being two said dampingmeans to each span of the transmission line conductor positionedrespectively at one third and two thirds of the distance along the span.

6. The combination claimed in claim 1, wherein saidof the span from thenearer of said points, each said damping means comprising a ridid bodycoupled to the conductor and spaced therefrom by a deformable bodysusceptible to torsional shear stresses, and means attached to the rigidbody for restraining torsional movements of the rigid body so as tocause torsional vibrational energy of the conductor to be dissipated bythe deformable body.

9. The combination claimed in claim 8, wherein the deformable body is ofbutyl rubber foam.

10. The combination claimed in claim 9, wherein said means forrestraining torsional movements of the rigid body comprises a weightsuspended from the rigid body.

11. In a transmission line conductor suspended from a stationary supportstructure to which it is connected at a plurality of longitudinallyspaced points, the suspended conductor defining a torsionallyoscillating system, the improvement in which the conductor consists of aplurality of strands coated with low friction material and looselyfitted within a sleeve of the low friction material.

12. In a transmission line conductor suspended from a stationary supportstructure to which it is connected at a plurality of longitudinallyspaced points, the suspended conductor defining a torsionallyoscillating system, the improvement in which the conductor consists of aplurality of strands coated with low friction material and looselyfitted within a sleeve of the low friction material, and an outer layerof strands extending along and engaging the outer surface of saidsleeve.

@ 33 XJUNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,778,527 I Dated December 11, 1973 Inventor(s) Qlaf- NigOl It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Change the wording of claim 2 to read as follows:

f-- The combination claimed in claim 1, wherein the first body comprises'a tubular metallic sleeve securedto the conductor, the" sleeve having acoating of low friction material defining said first surface, and thesecond body comprises a clamp which is clamped onto the sleeve, theclamp providing a sleeve-engaging surface which is coated with said: lowfriction material.

Signed and sealed this 6th day of August 1974.

(SEAL) Attest: v

MCCOY M. GIBSON, JR. I c. MARSHALL DANN Attesting Officer Commissionerof Patents izgizsgguv 11 mm!) STATES PATENT OFFICE CERTIFICATE OFCORRECTION latent No. 3,778,527 a d December 11, 1973 Inventor(s) OlafNigol It is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

Change the wording of claim 2 to read as follows:

f- The combination claimed in claim 1, wherein the first body comprisesa tubular metallic sleeve secured [to the conductor, theisleeve having acoating of low friction material defining said first surface,- and thesecond body comprisesa clamp which is clamped onto the sleeve, the clampproviding a sleeve-engaging surface which is coated with said lowfriction material.

Signed are sealed this 6th day of August 1974-.

(SEAL) Attest:

McCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents

1. In combination with a transmission line conductor suspended from astationary support structure to which it is connected at a plurality oflongitudinally spaced points, the suspended conductor defining atorsionally oscillating system, torsional damping means connected to theconductor at each span intermediate said spaced points at a distance notless than one third of the length of the span from the nearer of saidpoints, each said damping means comprising a first body rigidlyconnected to the conductor, the first body providing a first frictionalsurface arranged coaxially with the conductor, a second body connectedto the first body, the second body providing a second frictional surfacedisposed first body comprises a tubular metallic sleeve secured to theconductor, the sleeve having a coating of low friction material definingsaid first surface, and the second body comprises a clamp which isclamped onto the sleeve, the clamp providing a sleeve-engaging suracewhich is coated with said low frictional material. in sliding contactwith the first frictional surface, said first and second frictionalsurfaces being defined by coatings of low friction material on saidfirst and second bodies, and means attached to said second body forrestraining torsional movement of the second body so as to permitrelative sliding movements between said surfaces.
 2. The combinationclaimed in claim 1, wherein the
 3. The combination claimed in claim 2,wherein the clamp comprises a pair of hingedly connected clampingmembers secured by a spring-loaded adjustable bolt for adjustment of theclamping pressure.
 4. The combination claimed in claim 1, there beingone said damping means to each span of the transmission line conductorpositioned midway between a respective pair of said longitudinallyspaced points.
 5. The combination claimed in claim 1, there being twosaid damping means to each span of the transmission line conductorpositioned respectively at one Third and two thirds of the distancealong the span.
 6. The combination claimed in claim 1, wherein saidmeans for restraining torsional movements of the second body comprises aweight suspended from the second body.
 7. The combination claimed inclaim 1, wherein said low friction material is polytetrafluoroethylene.8. In combination with a transmission line conductor suspended from astationary support structure to which it is connected at a plurality oflongitudinally spaced points, the suspended conductor defining atorsionally oscillating system, torsional damping means connected to theconductor at each span intermediate said spaced points at a distance notless than one third of the length of the span from the nearer of saidpoints, each said damping means comprising a ridid body coupled to theconductor and spaced therefrom by a deformable body susceptible totorsional shear stresses, and means attached to the rigid body forrestraining torsional movements of the rigid body so as to causetorsional vibrational energy of the conductor to be dissipated by thedeformable body.
 9. The combination claimed in claim 8, wherein thedeformable body is of butyl rubber foam.
 10. The combination claimed inclaim 9, wherein said means for restraining torsional movements of therigid body comprises a weight suspended from the rigid body.
 11. In atransmission line conductor suspended from a stationary supportstructure to which it is connected at a plurality of longitudinallyspaced points, the suspended conductor defining a torsionallyoscillating system, the improvement in which the conductor consists of aplurality of strands coated with low friction material and looselyfitted within a sleeve of the low friction material.
 12. In atransmission line conductor suspended from a stationary supportstructure to which it is connected at a plurality of longitudinallyspaced points, the suspended conductor defining a torsionallyoscillating system, the improvement in which the conductor consists of aplurality of strands coated with low friction material and looselyfitted within a sleeve of the low friction material, and an outer layerof strands extending along and engaging the outer surface of saidsleeve.